Many vehicles, machines and other structures are constructed on an open frame, sometimes referred to as a space frame, out of elongate structural members such as solid or hollow struts. A space frame is typically a lightweight rigid structure constructed from interlocking struts, most often in a geometric pattern. Space frames can be used to span large areas with few interior supports such as columns. Like the truss, a space frame is strong because flexing loads and bending moments are transmitted as tension and compression vectors along the length of each strut. Space frames are common in building construction such as large roof spans in modern commercial and industrial buildings. Space frames have been used for a variety of vehicle chassis wherein the engine and body panels are suspended, and the body panels have little or no structural function.
At positions where the structural members intersect and form frame junctions, the members are typically cut at angles and coped to fit to each other. In order to attach coped tubular members to each other, jigs are employed to hold the tubes while joining, typically by welding or a similar process. Alternatively, hollow castings, which may be referred to as “lugs” or “nodes,” may be used at the frame junctions with the tubes fitted interiorly into the castings before welding, brazing, or soldering, for example. Hollow castings may obviate the need for the use of jigs to hold every element, but the tubes are still coped to maximize the insertion dimension of each tube into the casting. In such joining methods, there is a concentration of stress at the point of intersection of the tubes or of the tubes and the casting, especially at the weld. The set up and use of such jigs is time consuming. Also, the inspection of welds that are interior to a casting may be difficult or may require expensive test equipment.